With the recent revelations that alleged movie-theater shooter James Holmes had been seeing a psychiatrist prior to carrying out the July 20 massacre in Aurora, Colo., questions about the link between violence and mental illness have risen once again: What are the root causes of seemingly random violence? Does mental illness provoke it or predispose people to harm others?

Advocates for the mentally ill are faced with a deep dilemma each time extreme and deadly crimes are perpetrated by those with a mental illness. Obviously, such acts are not sane or normal; it beggars common sense to suggest that a person who is thinking straight would choose to kill or wound dozens of strangers. And yet most mentally ill people — even those with conditions that have been linked to violence, such as addictions and schizophrenia — are no threat to anyone other than themselves.

So how can we understand who is at risk for becoming violent without increasing the stigma associated with mental illness, especially when that stigma may account for a large part of the association between the two? Some data may help: people with schizophrenia — a disorder being studied by the psychiatrist who was treating Holmes — are roughly twice as likely to be violent as those who do not have the disorder, according to a 2009 review of research. People who have schizophrenia and a substance-use disorder are at even greater risk: they have a nine times higher risk of violence than people with neither disorder. The association is especially marked for homicide: those with schizophrenia are nearly 20 times as likely to kill another person as people unaffected by the disease.

However, the majority of people with schizophrenia (about 1% of the population) never commit acts of violence. A 2011 review of data on people who had suffered a first episode of psychosis — which is often a sign of schizophrenia (though psychosis is also associated with severe depression and amphetamine or marijuana misuse) — found that 35% had committed some type of violent act. That means that nearly two-thirds were nonviolent. Further, of those who did become violent, fewer than 1% had committed violence severe enough to result in hospitalization or permanent injury.

When looking at the rates of violent crime overall — homicide, for instance — the best estimate is that 5% to 10% of murders are committed by people with mental illness. But a far larger proportion of mass homicides, including the brutal July 2011 attacks in Norway, the Tucson, Ariz., shooting that wounded Congresswoman Gabby Giffords and the Virginia Tech massacre in 2007, involve perpetrators with mental illness. The proportion far outstrips the rates of mental illness in the population.

So what leads one person to violence but not another? In some cases, it may be the stigma of mental illness that provokes it, by exacerbating existing symptoms of delusion, disconnection from reality, social withdrawal and lack of emotion. A rare insight into the mind of a patient with schizophrenia comes from a former academic who wrote anonymously about her experience with social stigma from her disease (via writer David Dobbs at Wired). “N” writes:

I was diagnosed with schizophrenia just a month after Steven Kazmierczak (quickly identified as “schizoaffective”) shot six people to death on the campus of [Northern Illinois University] … Undoubtedly primed by this shooting, wary, uncertain, without enough time to think, my doctoral adviser suspended my graduate assistantship, banned me from the university, and alerted all faculty, graduate students and staff to forward all emails [from me] to her and, under no circumstances, respond.

N writes that her adviser had been operating under the wrongheaded assumption that she was planning to plant a bomb on campus. Although the decision to suspend N’s position was reversed within a week, it triggered a downward spiral that ultimately resulted in her expulsion. She writes:

Friends — my doctoral cohort, as is often the case, were a close and tight-knit group — abandoned me overnight. Students and faculty passed me in the halls, staring ahead blankly as if I were an undergraduate they had never seen and would never see again. Parties were announced, talked about, and I was never invited. Never again.

The social rejection worsened her disease and she became afraid to interact with people, eventually ceasing to attend classes and campus functions:

For a while I struggled through classes, overwhelmed, perhaps in equal measure, by delusions and this new and unprecedented isolation. Voices took the places of both professors and friends. Following a hospitalization (and consequent withdrawal from a semester’s worth of classes), I descended into a state of the most stunning dysfunction, unable (or simply unmotivated) even to walk from my bed to the bathroom.

After a review by an academic committee, during which her formerly trusted professors said they saw no chance that she would ever succeed, N was dismissed from her program. She broke down:

Me: Everything I have ever been told was a lie. My one way out — of poverty, desperation, madness — was never more than an illusion. And then disbelief. And then, how will I ever explain this to anyone, to family, to old mentors? And then betrayal. No language this time, no thoughts; crying, crying for hours. Alcohol, unconsciousness, unbidden dreams. Even there: repeating their words, over and over and over again. Isolation so intense, there is no way I will ever bridge it. I am lost. Days go by, weeks.

Eventually:

I fixated on a single vision, me, sometimes hanging, sometimes with gun in hand and a pool of blood on the floor, outside [her former adviser’s] office. Suicide, yes, obviously, but also something more: revenge.

Although N did not plan a mass killing, she writes that she understands how someone in Holmes’ situation — a former academic superstar and Ph.D. student in neuroscience, who had withdrawn from his program in June after a reportedly dismal performance on an oral exam — might have become so unhinged.

Dobbs points out in Wired that outcomes for people with schizophrenia may depend heavily on the patient’s cultural milieu: research conducted in the 1970s by the World Health Organization found that while 40% of people with schizophrenia in industrialized countries had severe impairments, less than a quarter of those in the developing world did and that over time, the disease followed a less devastating course in countries without advanced medical treatment.

The difference appears to rest on whether the larger culture views the disorder as a permanent affliction that destroys the person or, by contrast, as a brief possession by bad spirits. In the latter case, families and friends tend to accept affected people, letting them marry and work. (Of course, people with schizophrenia who live in cultures that stigmatize and reject those afflicted by bad spirits may get the worst of both worlds.)

Later studies have shown that medical treatment does improve outcomes in people with schizophrenia — indeed, appropriate medical treatment in the West has been shown to essentially eliminate patients’ risk of violence — but it’s clear that social support and the cultural environment clearly matter, not only when it comes to violence perpetrated by the mentally ill but also to violent crime in general.

As Eric Michael Johnson writes for Scientific American, the biggest contributor to homicide in the U.S. is not mental illness, addictions or even the accessibility of guns. It’s economic disparity: the wider the gap between the rich and poor, the more violence a population breeds. Describing an analysis of homicide rates in 50 states conducted by Harvard’s Ichiro Kawachi, Johnson writes:

The results were unambiguous: when income inequality was higher, so was the rate of homicide. Income inequality alone explained 74% of the variance in murder rates and half of the aggravated assaults. However, social capital had an even stronger association and, by itself, accounted for 82% of homicides and 61% of assaults. Other factors such as unemployment, poverty, or number of high school graduates were only weakly associated and alcohol consumption had no connection to violent crime at all. A World Bank sponsored study subsequently confirmed these results on income inequality concluding that, worldwide, homicide and the unequal distribution of resources are inextricably tied.

In other words, the connections we have to one another — our social capital, our ability to seek and receive support from others — is the most important weapon we have against violence. These connections are put at risk when economic inequality rises. Studies show that social cohesion and trust drop when disparities between the rich and poor rise. Since markets rely on trust to function smoothly — and since distrust can provoke political paralysis and polarization — a vicious cycle can ensue.

For the mentally ill, who might be seen as canaries in this coal mine, stigma serves to wall them off from the social support and medical care that are necessary to spur recovery and prevent illness from leading to tragedy. As a society, we need to understand that risk does not equal destiny — and that believing it does is a self-fulfilling prophecy. It’s not wrong to see schizophrenia as a disease or even to appreciate its association with violence, but to view people with schizophrenia as hopeless can in some cases worsen their course unnecessarily.

Indeed, the greatest individual risk factor for violence is not mental illness but gender — another characteristic over which people have no control. Schizophrenia doubles your odds of becoming violent, but being a man multiplies your risk by a factor of nine. Yet we don’t stigmatize or reject men for this risk factor; similarly, we shouldn’t treat the mentally ill that way. To prevent future catastrophes, we need to understand the range of cultural, social and medical factors that affect us all.

Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.